The proposed study, the Mexican Health and Aging Study-II (MHAS-II), aims to design and field the 3rd and 4th waves of survey data collection in Mexico. The two waves will be fielded in 2012 and 2014, eleven years after the two previous waves funded by NIA/NIH were fielded in 2001 and 2003. Funds are sought also to archive, document, and disseminate for public use the 3rd and 4th rounds as well as the resulting integrated data base containing all four waves. The previous study (MHAS-I) aimed to create a longitudinal prospective study of Mexican aging, starting with a national sample of persons aged 50 and older, using study protocols and survey instruments that were highly comparable to the U.S. Health and Retirement Study. In addition, the study design anticipated the need to examine long term implications for health and aging of the massive migration flows across the Mexico-U.S. border. Thus, the sample design included an over-sample in 6 states of Mexico with historically high levels of migration to the United States. MHAS-I had these and other unique features that MHAS-II will replicate and improve in the 3rd and 4th waves. New emphasis areas will be the study of aging in a mixed infectious-chronic epidemiological regime; assessment of the quality of self-report; the continuous culture of Mexico-U.S. migration and its consequences for aging; and the impact of a recent health sector reform in Mexico. This application has the following aims: 1) To carry out a third and fourth waves retaining the original substance of MHAS and adding the new content, following the survivors of waves 1 and 2 and refreshing the sample to yield again (as of wave 3) a representative cross section of the Mexican population aged 50 and over. 2) To enhance data distribution, dissemination, and outreach activities, to expand the knowledge about and use of the data sets and products of the four waves of the Mexican Health and Aging Study. User-friendly web-based platforms that have become available in the last ten years will be employed to provide enhanced public access to the data and project documentation. While the previous MHAS-I provided two waves of data spanning over two years, the analytical significance of the MHAS-II data will be much higher, forming a unique longitudinal study of four waves that span over thirteen years. The new data will enable enhanced research on aging and related population changes: of physical and mental health and disability, health behaviors and health care use, family support, aging and the life course, wealth, income, labor and retirement, migration and old age, and mortality, in a developing country aging fast with limited institutional support for individuals in old age. The data will enable cross-period and cross-cohort analyses of health and aging, and will be highly comparable with other similar studies in developed and developing countries, in particular the United States, enhancing the study of aging and health with a cross-national perspective.